The candidate's long term goals are to be an independent translational investigator and to improve the safety of blood transfusion by understanding mechanisms of immunosuppressive effects of stored red blood cells (RBCs). The objectives of this proposal are to provide the candidate with early translational research training and to determine the role of microRNA as mediators of red blood cell storage-related innate immune suppression. Innate immune suppression is common in critically ill children and is associated with adverse outcomes. Up to 49% of children who are in the intensive care unit for greater than 48 hours will receive an RBC transfusion. RBC transfusion has been shown to be immunosuppressive through unknown mechanisms. Older stored RBCs suppress innate immune cell (monocyte) function in vitro via heat-stable, soluble mediators capable of interfering with pro-inflammatory cytokine production at the mRNA level. MicroRNA (miRNA) is small, heat- stable, non-coding RNA capable of regulating multiple genes. RBCs contain miRNA and the relative abundance of specific miRNA may change over time during RBC storage. The central hypothesis of this proposal is that stored RBCs suppress monocyte function via the action of specific miRNA. Specific Aim one will comprehensively identify changes in RBC miRNA content over storage duration and determine changes in gene expression in monocytes after exposure to variably aged RBC products. A computational approach will be used to determine miRNA likely responsible for observed immunosuppressive effects of stored RBCs on monocytes. Specific Aim 2 will provide experimental evidence for immunosuppressive effects of specific miRNA. Specific Aim 3 will demonstrate the feasibility of a miRNA- targeted strategy to prevent RBC-induced monocyte suppression. The work described in this submission will lend novel mechanistic insights into RBC transfusion-related innate immune suppression. The conduct of these studies and specific instruction in basic science techniques, molecular immunology, microRNA biology, biostatistics, bioinformatics, and transfusion medicine will support the candidate's transition to independence.